A polycarbonate resin (hereinafter sometimes abbreviated as “PC resin”) is excellent in, for example, transparency, mechanical characteristics, thermal stability, electrical properties, and weatherability, and hence has been used in an optical molded article, such as a light-guiding plate, a lens, or an optical disc, by taking advantage of such characteristics.
With regard to a polycarbonate resin having a branched structure out of such resins, in, for example, Patent Literature 1, there are disclosures of a branched polycarbonate using a branching agent of a siloxane tetrabranched structure that is not a cyclic structure and a method of producing the polycarbonate. In Patent Literature 2, there are disclosures of a branched polycarbonate using a hydrocarbon-based tetrafunctional branching agent and a method of producing the polycarbonate. In Patent Literature 3, there is a disclosure of a resin composition formed of a branching agent of a siloxane cyclic tetrabranched structure used in the present invention and an epoxy resin.
However, it cannot be said that the thermal stability of the branched polycarbonate resin disclosed in Patent Literature 1 is sufficient. In addition, the branching agent disclosed in Patent Literature 2 involves an industrial disadvantage because of the following reason. The branching agent is insoluble in dichloromethane or an oligomer/dichloromethane solution, and hence needs to be separately dissolved in an alkaline solution.